1. Field of the Invention
The present invention relates to a rotation control apparatus for controlling a rotating state of a motor such as a spindle motor for rotating an optical disk or the like.
2. Description of Background Information
Hitherto, rotation control of a motor such as a spindle motor has been performed by using a sync signal (synchronization signal) recorded on an optical disk, for example, at predetermined intervals together with information data to be reproduced, so that the sync signal corresponds to such information data. The sync signal is detected, and the periodic intervals at which the sync signal is detected are compared with a reference signal having a predetermined constant period (the period is set at a value at which the recorded information is reproduced in the best state when the optical disk or the like is rotated according to that period). The rotational speed of the motor is controlled so that a difference between them is equal to zero, namely, the period of the sync signal detected coincides with the period of the reference signal.
In conventional rotation control apparatuses briefly described above, it is however a prerequisite that the sync signal is recorded at predetermined constant intervals (period). In the case of an optical disk or the like having such a structure wherein parts of the sync signal are recorded at intervals different from those of the other sync signal parts, with the conventional rotation control apparatus and phase sync circuit, it is impossible to maintain an accurate rotating state such as the CLV (Constant Linear Velocity) or CAV (Constant Angular Velocity) type rotation.
More particularly, if the conventional rotation control apparatus is applied to the optical disk or the like such that parts of the sync signal are recorded at an interval corresponding to a period different from the period of the other sync signal parts, even the interval of the sync signal parts different from the intervals of the other sync signal parts is also controlled so as to be matched with the period (corresponding to the intervals of the other sync signal parts) of the reference signal. When the portion where the interval of the sync signal parts is different from the intervals of the other sync signal parts is detected, therefore, the rotational speed is deviated (being faster or delayed) from the rotational speed to be obtained by a value corresponding to the difference between the intervals of the sync signal. Namely, there arises a problem that the operation to control the rotation at the period of the reference signal contrarily causes a fluctuation of the rotation.
The invention, therefore, has been made in consideration of the foregoing problems and it is an object of the invention to provide a rotation control apparatus which can maintain an accurate rotating state even in an information recording medium wherein a part of the sync signal is recorded at an interval different from those of the other sync signal parts.
To accomplish the above objects, according to the first aspect of the invention there is provided a rotation control apparatus for controlling a rotation of an information recording medium having pre-pits which are formed at periodic intervals having a period that is m (m is an integer) times a unit period in accordance with pre-information to be recorded and are recorded at positions that are deviated from the periodic intervals by an interval that is k (k is an integer smaller than m (k less than m)) times the unit period depending on recording positions of the pre-pits, comprising: a unit period signal generator which generates a unit period signal having the unit period; a pre-pit detector which detects the pre-pits from the recording medium; phase difference detector which detects a phase difference between a detection timing of the pre-pits and the unit period signal and generating a phase difference signal; a holding circuit for holding the phase difference signal; a rotation control device which receives said phase difference signal, wherein the rotation of the recording medium is controlled on the basis of the phase difference signal held by the holding circuit.
According to the first aspect of the invention, the unit period signal generator generates the unit period signal having a unit period that is a fraction (by the division by an integer number) of the period of intervals at which the pre-pits constituted by a sync pre-signal and a data pre-signal are recorded, and supplies the unit period signal to the phase comparator.
In parallel with the above operation, the pre-pit detector detects the pre-pits from the recording medium and supplies a detection signal indicating the detection of the pre-pits to the phase comparator.
The phase comparator executes a phase comparison with the unit period signal at timings when the detection signal is supplied, thereby generating a phase difference signal indicative of a fluctuation amount in the unit period of the detection timing of the pre-pit.
The holding circuit holds the phase difference signal which is supplied from the phase comparator until a next phase difference signal is supplied.
On the basis of the phase difference signal being held by the holding circuit, the phase difference is set off and the rotation of the motor is controlled so as to put it into a predetermined rotating state.
Thus, the rotation of-the motor is controlled in such a way that a phase difference for the unit period as a period of a fraction of the period of the intervals of the pre-pits is compared at detection timings of pre-pits, and the control of the motor rotation is effected to set off the phase difference. Even when the pre-pits are not derived at predetermined periodic intervals, therefore, a predetermined rotational state can be accurately obtained.
To accomplish the objects described, the second aspect of the invention features that, in the rotation control apparatus according to the first aspect of the invention, the unit period signal generator generates a monotonous increasing signal having the unit period, and the phase difference detector detects the phase difference on the basis of an amplitude value of the monotonous increasing signal at the detection timings of the pre-pits.
To accomplish the above objects, according to the third aspect of the invention there is provided a rotation control apparatus for controlling a rotation of an information recording medium having pre-pits constituted by sync pits which are formed at first periodic intervals having a period in relation to the unit period such that it is m (m is an integer) times a unit period and are recorded at positions that are deviated from the first period interval by an interval that is k (k is an integer; k less than m) times the unit period depending on recording positions, and information pits which are recorded at second periodic intervals having a period which is smaller than the period of the first periodic intervals and is in relation to the unit period such that it is n times the unit period in accordance with pre-information to be recorded, comprising: a unit period signal generator which generates a unit period signal having the unit period; a pre-pit detector which detects the pre-pits from the recording medium; a sync pit detector which detects the sync pits from the pre-pits; a first phase difference detector which detects a phase difference between detection timings of the sync pits and the unit period signal; a second phase difference detector which detects a phase difference between the detection timings of the pre-pits and the unit period signal and generates a first phase difference signal; a first holding circuit which holds the first phase difference signal which is generated from the first phase difference detector; a second holding circuit which holds the second phase difference signal which is generated from the second phase difference detector; and an adder which adds the first and second phase difference signals held at the first holding circuit and the second holding circuit, and a rotation control device which receives an output signal of the adder, wherein the rotation of the recording medium is controlled on the basis of an output signal of the adder.
According to the third aspect of the invention, the unit period signal generator generates the unit period signal having the unit period which is a fraction of the period of the intervals at which the pre-pits constituted by the sync pre-signals and data pre-signals are recorded and supplies the unit period signal to the first and second phase comparator.
In parallel with the above operation, the pre-pit detector detects the pre-pit from the recording medium and supplies a detection signal notifying the detection of the pre-pit to the second phase comparator.
The sync pit detector detects the sync pits from the pre-pits and supplies a detection signal notifying the detection of the sync pit to the first comparator.
The first phase comparator performs a phase comparison with the unit period signal at the detection timings of the sync pits and generates a first phase difference signal indicative of a fluctuation amount in the unit period of the detection timings of the sync pits.
The first holding circuit holds the first phase difference signal which is supplied from the first phase comparator until a next phase difference signal is supplied, and supplies the phase difference signal being held to the adder.
The second holding circuit holds the second phase difference signal which is supplied from the second phase comparator until a next phase difference signal is supplied and supplies the phase difference signal held to the adder.
The adder generates an addition phase difference signal in which the first and second phase difference signals being supplied are added.
On the basis of the addition phase difference signal which is supplied from the adder, the phase difference is set off and the motor rotation is controlled so as to enter a predetermined rotating state.
Thus, a coarse phase difference signal is obtained by comparing the phase difference for the unit period as a period that is a fraction of the period of the intervals of the sync pits at a detection timing of the sync pits which are detected at relatively coarse intervals, a fine phase difference signal is obtained by comparing the phase difference for the unit period as a period which is a fraction of the period of the intervals of the pre-pits at detection timings of the pre-pits which are detected at relatively dense intervals comprising the sync pre-signals and data pre-signals, and an addition phase difference signal is produced by adding the coarse phase difference signal and the fine phase difference signal. The motor rotation is controlled so as to set off those phase differences. Therefore, even when no pre-pit is derived at predetermined periodic intervals, a predetermined rotating state can be accurately obtained and as compared with the rotation control performed by using the sync pits only, so that a rotation control of a higher precision can be executed.